Method for polishing a semiconductor wafer

ABSTRACT

An apparatus for polishing a wafer comprises a supporting portion having an abrasive pad disposed thereon, and a polishing head disposed over the abrasive pad. The polishing head comprises a carrier having at least two fluid passages, a retainer ring disposed on a lower edge of the carrier, forming a space for receiving the wafer, a supporter disposed in the carrier, and a flexible membrane disposed to be in contact with the wafer. The supporter has an upper surface portion, a lower surface portion, a plurality of first holes, a plurality of second holes, and a first chamber. The upper surface portion of the supporter forms a second chamber along with an inner surface of the carrier. The second chamber is in communication with one of the two fluid passages of the carrier and the second holes are formed in a lower surface portion of the supporter to communicate with the second chamber. The first chamber is in communication with the other one of the two fluid passages and the first holes are formed in the lower surface portion of the supporter to communicate with the first chamber. The lower surface portion of the supporter has a flat surface and a chamfered or rounded edge. The membrane disposed to enclose the lower surface portion of the supporter has a plurality of third holes formed at positions corresponding to the first holes to absorb and hold the wafer by vacuum.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 11/052,275, filed Feb. 7, 2005, now U.S. Pat. No. 7,081,045, whichis a divisional of U.S. application Ser. No. 10/670,855, filed Sep. 25,2003, now U.S. Pat. No. 6,921,323, which is a divisional application ofSer. No. 09/877,922, filed Jun. 7, 2001, now U.S. Pat. No. 6,652,362,which relies for priority upon Korean Patent Application No. 2000-69983,filed on Nov. 23, 2000 and Korean Patent Application No. 2001-11055,filed on Mar. 3, 2001, the contents of which are herein incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to an apparatus for manufacturing asemiconductor wafer and method therefor, and more particularly to anapparatus for polishing a semiconductor wafer and method therefor.

BACKGROUND OF THE INVENTION

As the elements incorporated into a semiconductor device areincreasingly integrated, the structure of device wires such as gatelines and bit lines continues to become multiple-layered. For thisreason, step coverage between unit cells on a semiconductor substrate isincreased. To reduce the step coverage between the unit cells, variousmethods of polishing a wafer have been developed. Among these methods, achemical-mechanical polishing (CMP) method which planarizes the surfaceof the wafer in the fabrication is widely used.

In a general CMP process, a polishing head of a CMP apparatus secures awafer using a vacuum or surface tension and loads the wafer on anabrasive pad of a turntable. The polishing head imposes a controllableload on the wafer to hold it in tight contact with the abrasive pad.Thereafter, the polishing head is rotated to rotate the wafer withrespect to the abrasive pad of the turntable.

In order to increase the efficiency of the CMP process, the wafer shouldbe polished at a high speed while maintaining uniform flatness. However,characteristics such as uniformity, flatness and polishing speed of thewafer are highly dependent on relative speed between the wafer and theabrasive pad, as well as the force or load of the polishing head urgingthe wafer against the abrasive pad. Particularly, the larger the forceimposed on the wafer by the polishing head against the abrasive pad, thefaster the polishing speed. Accordingly, in the case where an unevenload is imposed on the wafer by means of the polishing head, a portionof the wafer on which relatively large force is imposed will be polishedat a faster rate than other portions of the wafer on which relativelysmall force is imposed.

Generally, the polishing head includes a flexible membrane which isadapted to pick up and release the by vacuum. However, the vacuumbetween the membrane and the wafer is often leaked, such that duringtransfer, the wafer may be dropped or otherwise harmed.

To address these limitations, a polishing head with a modified structurehas been proposed, which chucks/releases a wafer via vacuum holes formedat bosses that protrude from a chucking supporter of the head. However,such a polishing head introduces limitations that are shown in FIG. 1,which is a graph illustrating the resulting uneven surface of a wafer.In FIG. 1, reference character A indicates a wafer portion correspondingto the protruded bosses and reference character B indicates a wafercorresponding to a step projected from an edge of the supporter.Portions A and B are relatively over-polished as compared to otherportion of the wafer, thereby compromising the uniformity of polishingsurface of the wafer.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedapparatus for polishing a semiconductor wafer and method therefor whichcan provide high polishing uniformity.

It is another object of the present invention to provide an improvedapparatus for polishing a semiconductor wafer and method therefor whichcan individually control pressure to be imposed on each of certain areasof the wafer in a polishing process.

It is other object of the present invention to provide an improvedapparatus for polishing a semiconductor wafer and method therefor whichcan individually control polishing speed of each of certain areas of thewafer in a polishing process.

It is further object of the present invention to provide an improvedapparatus for polishing a semiconductor wafer and method therefor,having a polishing head which can stably pick up the wafer.

It is still other object of the present invention to provide an improvedapparatus for polishing a semiconductor wafer and method therefor, whichcan prevent scratches from being generated by the polishing head due tocleansing slurry particles flowing between membranes and supportersduring the polishing process.

These and other objects are provided, according to the presentinvention, by an apparatus for polishing a semiconductor wafercomprising a supporting portion having an abrasive pad disposed thereon,and a polishing head disposed over the abrasive pad. The polishing headcomprises a dish shaped carrier, a retainer ring disposed on a loweredge of the carrier, a supporter disposed in the carrier to providefirst and second chambers separated from each other, and a membraneenclosing a surface portion of the supporter to be able to be expandedand spaced apart from the surface portion.

In a preferred embodiment, the surface portion of the supporter has aflat surface and a plurality of first and second holes formed therein tocommunicate with the first and second chambers. The membrane has aplurality of third holes corresponding to the first holes.

Films are adhered on the flat surface around the first holes. Each ofthe films is sized so as to be inserted into the corresponding thirdhole and thickness less than, or equal to, that of the membrane. Also,an edge of the surface portion of the supporter can be chamfered orrounded.

In the embodiment, one of the second holes is formed in a center portionof said supporter, and there is no hole formed in a portion of themembrane corresponding to the one second hole.

According to another aspect of the present invention, there is providedan apparatus for polishing a wafer including a polishing headcomprising: a carrier, a retainer ring disposed on a lower edge of thecarrier, a supporter disposed in the carrier to provide a first chamber,a membrane enclosing a surface portion of the supporter to be able to beexpanded and spaced apart from the surface portion, and a chucking ringfor taking the wafer up by vacuum disposed on a lower portion thecarrier to provide a second chamber.

In a preferred embodiment, the supporter has a plurality of first holesformed in a surface portion thereof to communicate with the firstchamber, and the chucking ring has a plurality of second holes formedtherein to communicate with the second chamber. Films are adhered on thechucking ring around the second holes to act as a medium in taking up ortaking up and releasing of the wafer. The first and second chambers canhave first and second fluid passages communicating external to thepolishing head.

In the embodiment, the polishing head further includes a manifold forsupplying air or fluid, or vacuum, from the outside of the polishinghead to the first and second fluid passages, and a first elastic memberfor moving elastically the carrier up and down by means of air or vacuumsupplied from the manifold, disposed between the manifold and thecarrier.

According to other aspect of the present invention, there is provided anapparatus for polishing a semiconductor wafer including a polishing headcomprising: a dish shaped carrier, a retainer ring disposed on an loweredge of the polishing head, having a space for receiving the wafer, acenter supporter disposed in the carrier to provide a first chamber, amiddle supporter disposed in the carrier on the same plane as the centersupporter is disposed, to provide a second chamber, first and secondmembranes enclosing the center and middle supporters to be able to beseparated from surface portions of the supporters, and a chucking ringdisposed in the carrier to provide a third chamber.

In a preferred embodiment, a plurality of first holes are formed in thesurface portion of the center supporter to communicate with the firstchamber, a plurality of second holes are formed in the surface portionof the middle supporter to communicate with the second chamber, and aplurality of third holes are formed in the chucking ring to communicatewith the third chamber.

In the embodiment, the chucking ring can be disposed between the centersupporter and the middle supporter. Alternatively, the chucking ring canbe disposed between the middle supporter and an inner surface of thecarrier. The first, second and third chambers can have first, second andthird fluid passages communicating external to the polishing head,respectively. Also, the middle supporter and the second membrane can becomposed of ring shapes.

According to further aspect of the present invention, there is provideda method for polishing a wafer for use in an apparatus comprising asupporting portion having an abrasive pad disposed thereon; a polishinghead disposed over the abrasive pad; and the polishing head comprising acarrier, a supporter disposed in the carrier to provide first and secondchambers separated from each other, including a surface portion having aflat surface and a plurality of first and second holes formed therein tocommunicate with the first and second chambers, and a membrane enclosinga surface portion of the supporter to be able to be expanded and spacedapart from the surface portion, having a plurality of third holescorresponding to the first holes, comprising the step of positioning themembrane on a first surface of the wafer, taking the wafer up by makingthe first and second chambers communicating with the first and secondholes vacuous or respectively vacuous and at atmospheric pressure toabsorb and hold the wafer through the third holes, positioning the waferon the abrasive pad to allow a second surface of the wafer to be incontact with the abrasive pad, expanding the membrane to impose load onthe wafer by inputting air into the membrane through the first andsecond holes into the membrane, and polishing the second surface of thewafer by rotating the polishing head.

The method further includes the steps drawing the wafer upwardly bymaking the first and second chambers communicating with the first andsecond holes vacuous, or, respectively vacuous and at atmosphericpressure, to absorb and hold the wafer through is the third holes afterthe polishing step, and unloading the wafer from the polishing pad.

According to still other aspect of the present invention, there isprovided a method for polishing a wafer for use in an apparatuscomprising a dish shaped carrier, a retainer ring disposed on an loweredge of the polishing head, having a space for receiving the wafer, acenter supporter disposed in the carrier to provide a first chambercommunicating with a plurality of first holes, a middle supporterdisposed in the carrier on the same plane as the center supporter isdisposed, to provide a second chamber communicating with a plurality ofsecond holes, first and second membranes enclosing the center and middlesupporters to be able to be separated from surface portions of thesupporters, and a chucking ring disposed in the carrier to provide athird chamber communicating with a plurality of third holes, comprisingthe step of positioning the chucking ring on a first surface of thewafer, drawing the wafer upwardly by making the first and secondchambers communicating with the first and second holes vacuous or atatmospheric pressure, and the third chamber communicating with the thirdholes vacuous to absorb and hold the wafer through the third holes,positioning the wafer on the abrasive pad to allow a second surface ofthe wafer to be in contact with the abrasive pad, expanding the firstand second membranes to impose load on the wafer by inputting air intothe first and second membranes through the first and second holes,inputting air through the third holes to impose pressure on the firstsurface of the wafer, and polishing the second surface of the wafer byrotating the polishing head.

The method further includes the steps of taking the wafer up by makingthe first and second chambers communicating with the first and secondholes vacuous or at atmospheric pressure, and the third chambercommunicating with the third holes vacuous to absorb and hold the waferthrough the third holes after the polishing step, and unloading thewafer from the polishing pad.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the more particular description ofpreferred embodiments of the invention, as illustrated in theaccompanying drawings in which like reference characters refer to thesame parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a graph showing an uneven polishing state of a wafer.

FIG. 2 is a perspective view of a CMP apparatus according to the presentinvention.

FIG. 3 is an exploded perspective view of a polishing head in accordancewith a preferred first embodiment of the present invention.

FIG. 4 is a perspective view of the polishing head shown in FIG. 3.

FIG. 5 is a cross-sectional view of the polishing head taken along line5—5 of FIG. 4.

FIG. 6 a to FIG. 6 c are cross-sectional views showing the process stepsof polishing the wafer by using the polishing head in accordance withthe first embodiment of the present invention.

FIG. 7 a is a cross-sectional view of a polishing head in accordancewith a preferred second embodiment of the present invention, showing astate where pressure is imposed on the wafer.

FIG. 7 b is a cross-sectional view of the polishing head of FIG. 7 a,showing a state where the wafer is upwardly drawn by vacuum.

FIG. 8 a is a cross-sectional view of a polishing head in accordancewith a preferred third embodiment of the present invention, showing astate where pressure is imposed on the wafer.

FIG. 8 b is a cross-sectional view of the polishing head of FIG. 8 a,showing a state where the wafer is upwardly drawn by vacuum.

FIG. 9 is a bottom view of the polishing head in accordance with thefirst embodiment of the present invention.

FIG. 10 a to FIG. 10 c are views showing a polishing head in accordancewith an alternative first embodiment of the present invention.

FIG. 11 a is a cross-sectional view of a polishing head in accordancewith a preferred fourth embodiment of the present invention, showing astate where pressure is imposed on the wafer.

FIG. 11 b is a cross-sectional view of the polishing head of FIG. 11 a,showing a state where the wafer upwardly drawn by vacuum.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiment set forth herein; rather, these embodiments are provided sothat this disclosure will be through and complete, and will fully coverthe scope of the invention to those skilled in the art. Like numbersrefer to like elements throughout.

Referring now to FIG. 2, a general apparatus for CMP 100 to which thepresent invention is applied includes a polishing station 110 and apolishing head assembly 120.

On the polishing station 110, a rotatable turntable 114 connected with adevice (not shown) for rotating the turntable is disposed. In apolishing process, the rotating device are rotated in about 50 to 80 RPM(revolutions per minute). The rotatable turntable 114 has an abrasivepad 112 mounted thereon. The abrasive pad 112 is composed of acircle-shaped plate of composite material having an uneven polishingsurface.

The polishing station 110 includes a device 116 for conditioning theabrasive pad 112 and a device 118 for supplying slurries on the surfaceof the abrasive pad 112. The slurries are composed, for example, of areaction reagent such as deionized water (DIW), abrasive particles suchas silicon dioxide, and a chemical reaction catalyst such as potassiumhydroxide for oxidation polishing. It is noted that since theconditioning device 116 and the slurry supplying device 118 are deviceswell-known in the art and not within the scope of the invention, theywill not be explained in detail in the present application.

The polishing head assembly 120 of the apparatus for CMP 100 includes apolishing head 130, a driving axis 122 and a motor 124. The polishinghead 130 functions to uniformly impose a downward pressure on a wafer 10and maintain the wafer 10 (not shown) in contact with the abrasive pad112. The polishing head 130 can be rotated in 40 to 70 RPM by means ofthe driving axis 122 coupled to the motor 124. The polishing head 130 isalso connected to two fluid channels, each of which are coupled to apump in order to supply air for pushing the wafer 10 or vacuum forcapturing and holding the wafer 10.

Embodiment 1

Referring to FIGS. 3 through 5, a polishing head 130 in accordance witha preferred first embodiment of the present invention includes amanifold 132, a dish-shaped carrier 134, a retainer ring 140, asupporter 150 and a flexible membrane 170. The manifold 132 is acomponent serving to connect the two fluid channels to first and secondfluid passages 134 a, 134 b, as shown in FIG. 5. The supporter 150disposed in the carrier 134 has an upper surface portion 152, a lowersurface portion 154, a plurality of first holes 156, a plurality ofsecond holes 158, and a first chamber 160. The upper surface portion 152of the supporter 150 forms a second chamber 136 along with an innersurface of the carrier 134. The second chamber 136 communicates with thesecond fluid passage 134 b of the carrier 134 and the second holes 158formed in the lower surface portion 154 of the supporter 150. The firstchamber 160 communicates with the first fluid passage 134 a and thefirst holes 156. The lower surface portion 154 of the supporter 150 hasa substantially planar flat surface or a substantially planar androunded edge surface. Alternatively, the edge 155 of the lower surfaceportion 154 can be chamfered. The structure of the lower surface portion154 includes a substantially planar flat surface and rounded edges inorder to impose a uniform load on a rear or first surface 10 a of thewafer 10 in a polishing process.

On the lower surface portion 154 of the supporter 150, films 164 areoptionally adhered to operate as a medium in drawing and releasing ofthe wafer 10. The films 164 are adhered to the lower surface portion 154of the supporter 150 in regions surrounding the first holes 156. Eachfilm 164 is sized such that it is capable of insertion in respectivecorresponding third holes 172 of the membrane 170 and is of the samethickness as that of the membrane 170. Alternatively, the thickness ofthe films 164 can be formed to be less than that of the membrane 170.

The membrane 170 preferably comprises a thin rubber film which is incontact with the rear surface 10A of the wafer 10. When gas or liquid,preferably air is inputted into the membrane 170, it is expanded toimpose uniformly load on the rear surface 10 a of the wafer 10. Themembrane 170 has a plurality of third holes 172 formed in portionsthereof corresponding to the first holes 156 to absorb and hold thewafer 10 under vacuum.

Under an edge of a lower end of the carrier 134, a retainer ring 140 isdisposed. The retainer ring 140 operates to prevent the wafer 10 fromescaping from the polishing head 130 during polishing.

A wafer polishing process of an apparatus for CMP 100 having a polishinghead 130 in accordance with the first embodiment of the presentinvention will now be described. The polishing process comprises thesteps of loading a wafer 10 on an abrasive pad 112 of a turntable 114 bymeans of a polishing head 130, polishing a front or second surface 10 bof the wafer 10 by imposing an air pressure on a membrane 170, chuckingthe wafer 10 by means of the polishing head 130, and unloading the wafer10 on a stand-by stage (not shown) from the abrasive pad 112 of theturntable 114.

The steps of the polishing process will be explained in detail withreference to the following table.

TABLE 1 The first chamber The second chamber Loading step Vacuum Zero orvacuum Polishing step Pressure Pressure Chucking step Vacuum Zero orvacuum Unloading step Pressure Any one of pressure, zero, vacuum (Ifpossible, pressure)

Referring to the table 1, in the loading step, the polishing head 130 ismoved to bring the membrane 170 in contact with the rear surface 10 a ofthe wafer 10. Then, gas, preferably air, is output, or discharged,through a first fluid passage 134 a to make a first chamber 160 vacuous,and through a second fluid passage 134 b to make a second chamber 136 atatmospheric pressure (called “zero” in the art) or vacuous. As a result,the wafer 10 is absorbed through first holes 156 of the supporter 150and third holes 172 of the membrane 170 by compressing the membrane 170against the underside of the supporter, as shown in FIG. 6 a. Next, thewafer 10 adhered to the membrane 170 by vacuum is loaded on the abrasivepad 112 of the turntable 114 by means of the polishing head 130. At thistime, the polishing head 130 is lowered until the wafer 10 is in contactin with the abrasive pad 112.

As shown in FIG. 6 b, during the polishing step, air is input into thefirst and second chambers 160, 136 through the first and second fluidpassages 134 a, 134 b. As a result, air pressure is provided through thefirst and second holes 156, 158 to the membrane 170 and thereby themembrane 170 is expanded, since the third holes 172 of the membrane 170are blocked by means of the wafer 10. Expanded membrane 170 provides auniform load over the entire rear surface 10 a of the wafer 10. In thisstate, slurries are supplied through slurry supplying device, and thepolishing head 130 and the turntable 114 are rotated in oppositedirections to each other to polish the front surface 10 b of the wafer10.

As shown in FIG. 6 c, during the chucking step following polishing, airis again discharged through the first fluid passage 134 a to make thefirst chamber 160 vacuous, and through the second fluid passage 134 b tomake the second chamber 136 at atmospheric pressure or vacuous. As aresult, the wafer 10 is absorbed through the first holes 156 of thesupporter 150 and the third holes 172 of the membrane 170 whilecompressing the membrane 170, and adhered thereto. Next, the wafer 10adhered to the membrane 170 by vacuum is unloaded on a stand-by stagefrom the abrasive pad 112 of the turntable 114 by means of the polishinghead 130. Thereafter, air is input into the first 10 and second chambers160, 136 through the first and second fluid passages 134 a, 134 b. As aresult, the wafer adhered to the membrane 170 by vacuum is released fromthe membrane 170.

After performing the polishing process, a cleaning process can becarried out to remove slurries that had flowed between the membrane 170and a lower surface portion 154 of the supporter 150. During thecleaning process, first, DIW and N₂ gas are continuously supplied intothe second chamber 136 through the second fluid passage 134 b. As aresult, DIW and N₂ gas flows between the membrane 170 and the lowersurface portion 154 of the supporter 150 through the second holes 158communicating with the second chamber 136, to clean the slurriestherebetween. Thus, the slurries are removed and thereby scratchesgenerated on the wafers during subsequent processes due to the remainingslurry particles can be minimized.

As explained above, the polishing head 130 in accordance with the firstembodiment of the present invention can prevent the wafer from beingdropped while capturing the wafer since it draws the wafer up byabsorbing and directly holding the wafer through the holes 172 of themembrane 170 by vacuum. Also, the problem of partial over-polishing ofthe wafer is eliminated since during the polishing step, the polishinghead can impose a uniform load on the rear surface of the wafer by thesubstantially flat surface, or the flat surface and rounded edge of thelower surface of the supporter.

FIG. 10 a to FIG. 10 c are views showing a polishing head 130 d inaccordance with a alternative example of the first embodiment of thepresent invention.

In the cleaning process of the polishing head 130 of the firstembodiment, DIW and N₂ gas are continuously supplied into the secondchamber 136 through the second fluid passage 134 b and then flowedbetween the membrane 170 and the lower surface portion 154 of thesupporter 150 through the second holes 158 communicating with the secondchamber 136 to clean remaining slurries therebetween. However, in thispolishing head 130, most DIW gas that flowed through the second holes158 is discharged through the third holes 172 adjacent to the secondholes 158 before arriving at a center portion indicated by region “C” ofthe FIG. 9. As a result, the cleaning effect at the center portion “C”;is not as thorough as compared with that at the circumference of thesecond holes 158 since the amount of cleansing DIW arriving at thecenter portion “C” is less. To solve the problem, the polishing head 130d of the transformed example of the first embodiment is provided.

Referring to FIG. 10 a through FIG. 10 c, the polishing head 130 d inaccordance with the transformed example of the first embodiment has asecond hole 158 formed at a center portion of a supporter 150 incommunication with a second chamber 136. However, in a membrane 170, ahole corresponding to the second hole 158 of the center portion of thesupporter 150 is not formed. Thus, in a polishing process, a sufficientamount of DIW and N₂ gas will flow into the center portion “C”, as wellas an edge portion, of the supporter 150, so that an uniform cleaningeffect can be obtained.

Since the structure of the remainder of the polishing head 130 d, (withthe exception of the second hole 158 of the center portion of thesupporter 150) is the same as that of the polishing head 130 of thefirst embodiment, it will not be explained in detail.

Embodiment 2

FIG. 7 a and FIG. 7 b illustrate cross-sections of a polishing head 130a in accordance with a preferred second embodiment of the presentinvention. The polishing head 130 a of the second embodiment isdifferent than the polishing head 130 of the first embodiment in thesense that the load can be individually controlled at both the supporter150 a and the retainer ring 140. Also, the polishing head 130 a has aseparate chucking ring for use in moving of the wafer.

Downward pressure of the retainer ring 140 is controlled by air suppliedthrough a third fluid passage 134 c of a manifold 132. For this, a firstelastic member 180 is disposed between the manifold 132 and a carrier134. The elastic member 180 is expanded or compressed by air suppliedthrough the third fluid passage 134 c to impose load on the carrier 134.The carrier 134 is coupled with the retainer ring 140 to impose adownward load thereto. The elastic member 180 is composed of syntheticrubber, so that it can be expanded or compressed between the manifold132 and the carrier 134 to buffer the carrier 134 and the retainer ring140.

Also, the polishing head 130 a includes a supporter 150 a for imposing auniformly distributed load on the wafer and a chucking ring 182 forcapturing the wafer by vacuum. A first chamber 160 of the supporter 150a is in communication with a first fluid passage 134 a in communicationwith the outside of the polishing head 130 a, and first holes 156 formedon a lower surface portion 154 of the supporter 150 a.

The chucking ring 182 forms a second chamber 136 communicating with asecond fluid passage 134 b along with an upper surface portion 152 ofthe supporter 150 a and an inner surface of the carrier 134. Thechucking ring 182 has a plurality of vacuum holes 184 for absorbing andholding the wafer by vacuum. On a lower surface of the chucking ring 182at which the vacuum holes 184 are formed, films 164 are adhered, asdescribed above. The films function as a medium for preventing scratchesbetween the chucking ring 182 and the wafer 10 during chucking andrelease of the wafer 10.

During polishing, gas, preferably air, is input through the first fluidpassages 134 a to provide air pressure for pushing the wafer 10, and incapturing the wafer, and is input through the second fluid passages 134b to form vacuum for absorbing and holding the wafer 10.

A wafer polishing process of an apparatus for CMP 100 having a polishinghead 130 a in accordance with the second embodiment of the presentinvention will now be described. The polishing process comprises thesteps of loading a wafer 10 on an abrasive pad 112 of a turntable 114 bymeans of a polishing head 130 a, polishing a front or second surface 10b of the wafer 10 by imposing an air pressure on a membrane 170 a,chucking the wafer 10 by means of the polishing head 130 a, andunloading the wafer 10 on a stand-by stage (not shown) from the abrasivepad 112 of the turntable 114.

The steps of the polishing process are explained in detail withreference to the following table.

TABLE 2 The second The third The first chamber chamber fluid passageLoading step Zero or vacuum Vacuum Pressure → zero Polishing stepPressure Pressure Pressure Chucking Zero or vacuum Vacuum Pressure →zero step Unloading Any one of Pressure Zero step Pressure, zero, andvacuum (If possible, pressure)

Referring to the table 2, during the loading step, the polishing head130 a is moved to allow the membrane 170 a to be in contact with therear surface 10 a of the wafer 10. Then, gas or liquid, preferably air,is discharged through a first fluid passage 134 a to make a firstchamber 160 vacuous or at atmospheric pressure, and through a secondfluid passage 134 b to make a second chamber 136 vacuous. At this time,through a third fluid passage 134 c, air is pumped to lower the carrier134 downward until the wafer 10 is completely absorbed and retained orchucked by vacuum. After drawing the wafer 10 in an upward direction,air is discharged through the third fluid passage 134 c to maintaindownward pressure of the carrier 134 at atmospheric pressure. As aresult, as shown in FIG. 7 b, the wafer 10 is absorbed and drawn byvacuum holes 184 of the chucking ring 182 while compressing the membrane170 a.

The wafer 10 is then loaded on the abrasive pad 112 of the turntable 114by means of the polishing head 130 a. At this time, the polishing head130 a is lowered until the wafer 10 is in contact in with the abrasivepad 112.

As shown in FIG. 7 a, during the polishing step, air is pumped into thefirst and second chambers 160, 136 and the first elastic member 180through the first, second and third fluid passages 134 a, 134 b, 134 c.As a result, the air pressure is provided through the 45 first holes 156to the membrane 170 a to expand the membrane 170 a, and through thevacuum holes 184 to an edge of the wafer 10 to impose a load thereon.The elastic member 180 is likewise expanded to impose load on thecarrier 134. In this state, slurries are supplied through slurrysupplying device 118, and the polishing head 130 a and the turntable 114are rotated in opposite directions to each other to polish the frontsurface 10 b of the wafer 10.

As shown in FIG. 7 b, during the chucking step after polishing, air isagain discharged through the first fluid passage 134 a to make the firstchamber 160 vacuous or at atmospheric pressure, and through the secondfluid passage 134 b to make the second chamber 136 vacuous. At thistime, air is pumped through the third fluid passage 134 c to lower thecarrier 134 downward until the wafer 10 is completely absorbed and drawnby vacuum. After drawing the wafer 10 up, air is discharged through thethird fluid passage 134 c to maintain downward pressure of the carrier134 at atmospheric pressure. As a result, the wafer 10 is absorbed anddrawn by the vacuum holes 184 of the chucking ring 182 while compressingthe membrane 170 a. Then, the wafer 10 drawn through the vacuum holes184 is unloaded on the stand-by stage from the abrasive pad 112 of theturntable 114 by means of the polishing head 130 a. Thereafter, air ispumped into the first and second chambers 160, 136 through the first andsecond fluid passages 134 a, 134 b. As a result, the wafer is separatedand released from the vacuum holes 184.

As explained above, the polishing head 130 a of the second embodiment ischaracterized in that it has a separate chucking ring 182 for drawingthe wafer up by vacuum. During the polishing process, the chucking ring182, through the vacuum hole 180 independently imposes a pressure on theedge of the wafer 10, while a pressure through the first hole 134 a isimposed on the center portion of the wafer 10. Also, the polishing head130 a can individually control load to be imposed on each of thesupporter 150 a and the retainer ring 140.

The structure and operation of the polishing head 130 a of the secondembodiment described above is otherwise the same as that of thepolishing head 130 of the first embodiment.

Embodiment 3

FIG. 8 a and FIG. 8 b show cross-sections of a polishing head 130 b inaccordance with a preferred third embodiment of the present invention.The polishing head 130 b of the third embodiment is different than thepolishing head 130 of the first embodiment in that it can individuallycontrol load to be imposed on each of first and second regions X1, X2,and also has a separate chucking ring for drawing the wafer as in thesecond embodiment.

The polishing head 130 b of the third embodiment includes a carrier 134,a center supporter 186, a middle supporter 188, a first membrane 192, asecond membrane 194 and a chucking ring 182.

The carrier 134 includes first, second, and third fluid passages 134 a,134 b, 134 c. The center supporter 186 has a first chamber 187communicating with the first fluid passage 134 a, and a lower surfaceportion having first holes 186 a to communicate with the first chamber187. Through the first fluid passage 134 a, air is pumped into the firstchamber 187 to impose load on a first area x1 of the wafer 10.

The middle supporter 188 disposed around the center supporter 186 in thecarrier 134 is positioned on the same plane as that of the centersupporter 186. The middle supporter 188 has a second chamber 189communicating with the second fluid passage 134 b, and a lower surfaceportion having second holes 188 a to communicate with the second chamber189. Through the second fluid passage 134 b, air is input into thesecond chamber 189 to force load on a second area x2 of the wafer 10.

The first and second membranes 192, 194 are adhered to edges of thecenter and middle supporters 186, 188 to enclose the lower surfaceportions thereof, respectively. The second membrane 194 enclosing themiddle supporter 188 and the lower surface portion thereof is composedof a ring shape.

Downward loads of the first and second membranes 192, 194 against thefirst and second areas X1, X2 of the wafer 10 are controlled by means ofair pressure in the first and second chamber 187, 189. Namely, loads ofthe first and second areas X1, X2 of the wafer 10 are controlled bychanging air pressures of the first and second fluid passages 134 a, 134b of the carrier 134.

Thus, the loads which are imposed on certain portions X1, X2 of thewafer 10 can be readily controlled and thereby relative polishing speedsof the certain portions X1, X2 of the wafer 10 can be more preciselycontrolled.

The chucking ring 182, along with an inner surface of the carrier 134and upper surfaces of the supporters 186, 188 forms a third chamber 183communicating with the third fluid passage 134 c. The chucking ring 182has vacuum holes 184 for drawing the wafer up by vacuum. On a lowersurface of the chucking ring 182 in which the vacuum holes 184 areformed, films 164 are adhered. The films 164 operate as a medium forpreventing scratches of the wafer 10 due to the chucking ring 182 inchucking and releasing of the wafer 10.

A wafer polishing process of an apparatus for CMP 100 having a polishinghead 130 b in accordance with the third embodiment of the presentinvention will now be described. The polishing process comprises thesteps of loading a wafer 10 on an abrasive pad 112 of a turntable 114 bymeans of a polishing head 130 b, polishing a front or second surface 10b of the wafer 10 by imposing air pressure on first and second membranes192, 194, chucking the wafer 10 by means of the polishing head 130 b,and unloading the wafer 10 on a stand-by stage (not shown) from theabrasive pad 112 of the turntable 114.

The steps of the polishing process are now explained in detail withreference to the following table.

TABLE 3 The first and second chamber The third chamber Loading step Zeroor vacuum Vacuum Polishing step Pressure Pressure Chucking step Zero orvacuum Vacuum Unloading Any one of Pressure, zero, and Pressure stepvacuum (If possible, pressure)

Referring to the table 3, in the loading step, the polishing head 130 bis moved to allow the first and second membranes 192,194 to be incontact with the rear surface 10 a of the wafer 10. Then, gas,preferably air, is discharged through first and second fluid passages134 a, 134 b to make the first and second chambers 187, 189 vacuous, orat atmospheric pressure, and through a third fluid passage 134 c to makea third chamber 183 vacuous. As a result, as shown in FIG. 8 b, thewafer 10 is absorbed and retained at vacuum holes 184 of a chucking ring182 while compressing the first and second membranes 192, 194.

The wafer 10 is next loaded on the abrasive pad 112 of the turntable 114by means of the polishing head 130 b. At this time, the polishing head130 b is lowered until the wafer 10 is in contact in with the abrasivepad 112.

As shown in FIG. 8 a, in the polishing step, air is individually inputinto the first, second and third chambers 187, 189, 183 through thefirst, second and third fluid passages 134 a, 134 b, 134 c. As a result,the air pressure is provided through the first and second holes 186 a,188 a to the first and second membranes 192, 194 to expand them, andthereby first and second spaces S1, S2 are formed between the centersupporter 186 and the first membrane 192 and between the middlesupporter 188 and the second membrane 194, respectively. Air pressure inthe first and second spaces S1, S2 forces the first and second areas X1,X2 of the wafer 10 to be pushed. Also, a slight load is imposed on anedge of the wafer 10 by means of air supplied through the vacuum holes184. In this state, slurries are supplied through slurry supplyingdevice 118, and the polishing head 130 b and turntable 114 are rotatedin opposite directions with respect to each other to polish the frontsurface 10 b of the wafer 10.

As shown in FIG. 8 b, during the chucking step after polishing, air isagain discharged through the first and second fluid passages 134 a, 134b to make the first and second chambers 187, 189 vacuous or atatmospheric pressure, and through the third fluid passage 134 c to makethe third chamber 183 vacuous. As a result, the wafer 10 is absorbed andchucked or took up through the vacuum holes 184 of the chucking ring 182while compressing the first and second membranes 192, 194. Next, thewafer 10 is unloaded on the stand-by stage from the abrasive pad 112 ofthe turntable 114 by means of the polishing head 130 b. Thereafter, airis input into the third chamber 183 through the third fluid passage 134c. As a result, the wafer is separated and released from the vacuumholes 184.

As explained above, the polishing head 130 b of the third embodiment ischaracterized in that it has a separate chucking ring 182 for taking thewafer up by vacuum and providing a space or a volume to impose a portionof the wafer 10 by supplying air through the first fluid passage 134 c.Also, the polishing head 130 b can individually control load to beimposed on certain portions of the wafer.

Also, it will be noted that in the polishing head 130 b of the thirdembodiment, membranes are disposed respectively on the center and middlesupporters, but plural membranes can be disposed on one supporter orconversely one membrane is disposed on plural supporters. Also, spacesformed by means of one or plural membranes and supporters respectivelycommunicate with corresponding fluid passages to individually controlthe air pressure therein.

Embodiment 4

FIG. 11 a and FIG. 11 b show cross-sections of a polishing head 130 c inaccordance with a preferred fourth embodiment of the present invention.The polishing head 130 c of the fourth embodiment is characterized inthat it can individually control load to be imposed on each of first,second and third areas X1, X2, X3, and has a chucking ring for takingthe wafer up. The chucking ring 182 is disposed between supportershaving improved lower surface portions.

Referring to FIG. 11 a, the polishing head 130 c of the fourthembodiment includes a carrier 134, a center supporter 186, an endsupporter 196, a first membrane 192, a second membrane 194 and achucking ring 182.

The carrier 134 has first, second, and third fluid passages 134 a, 134b, 134 c. The center supporter 186 has a first chamber 187 communicatingwith the first fluid passage 134 a, and a lower surface portion of thecenter supporter having first holes 186 a to communicate with the firstchamber 187. Through the first fluid passage 134 a, air is input intothe first chamber 187 to force a load on a first area X1 of the wafer10.

The chucking ring 182 disposed about the center supporter 186 in thecarrier 134 is positioned on the same plane as that of the centersupporter 186.

The end supporter 196 is disposed around the chucking ring 182 in thecarrier 134 and positioned on the same plane as that of the centersupporter 186. The end supporter 196 has a second chamber 197communicating with the second fluid passage 134 b, and a lower surfaceportion having second holes 196 a to communicate with the second chamber197. Through the second fluid passage 134 b, air is input into thesecond chamber 196 to force a load on a second area X2 of the wafer 10.

Each of the lower surface portions of the center and end supporters 186,196 is a flat surface having a rounded edge. Alternatively, edges of thelower surface portions can be chamfered. The structure of the lowersurface portions having flat surfaces and rounded edges functions toimpose uniformly load on a rear or first surface 10 a of the wafer 10during a polishing process.

The chucking ring 182 along with an inner surface of the carrier 134 andupper surfaces of the supporters 186, 196 forms a third chamber 183communicating with the third fluid passage 134 c. The chucking ring 182has vacuum holes 184 for taking the wafer up by vacuum. On a lowersurface of the chucking ring 182 in which the vacuum holes 184 areformed, films 164 are disposed. The films 164 operate as a medium forpreventing scratches of the wafer 10 due to the chucking ring 182 duringchucking and releasing of the wafer 10.

The first and second membranes 192, 194 are disposed at the edges of thecenter and end supporters 186, 196 to enclose the lower surface portionsthereof, respectively. The second membrane 194 enclosing the endsupporter 196 and the lower surface portion thereof is composed of aring shape.

As shown in FIG. 11 b, when air is individually pumped into the firstand second chambers 187, 197 through the first and second fluid passages134 a, 134 b, air pressure is provided through the first and secondholes 186 a, 196 a to the first and second membranes 192, 194 to expandthem, and thereby first and second spaces or volumes S1, S2 are formedbetween the center supporter 186 and the first membrane 192 and betweenthe end supporter 196 and the second membrane 194, respectively. At thistime, between the chucking ring 182 and the wafer 10, a third space orvolume S3 is formed by means of the first and second membranes 192, 194.Thus, the polishing head 130 c of this embodiment is characterized inthat a separate chucking ring 182 is operated by air, and the thirdspace S3 is formed spontaneously by expanding the first and secondmembranes 192, 194. Also, air pressures of the spaces S1, S2, S3 can beindividually controlled by means of the first, second, and third fluidpassages 134 a, 134 b, 134 c, respectively.

During a polishing step, downward loads against the first, second, andthird areas X1, X2, X3 of the wafer 10 can be controlled by means of airpressures in the first, second and third chambers 187, 197, 183. Namely,air supplied to the first and second chambers 187, 197 flows into thefirst and second membranes 192, 194 and expands them to form the firstand second spaces S1, S2 providing load against the first and secondareas X1, X2 of the wafer 10, and air supplied to the third chamber 183flows into the third space S3 between the first and second membranes192, 194 to provide load against the third area X3 of the wafer 10.Thus, the loads which are imposed on certain portions X1, X2, X3 of thewafer 10 can be easily controlled by changing pressures of air suppliedthrough the fluid passages 134 a, 134 b, 134 c of the carrier 134 andthereby polishing speed, or removal rate, of the certain portions X1,X2, X3 of the wafer 10 can be more precisely controlled.

Films 164 disposed as a medium in the first, second, third and fourthembodiments are optional.

The remaining structure and operation of the polishing head 130 cdescribed above is the same as that of the polishing heads of the firstand second embodiments.

As apparent from the foregoing description, it can be appreciated thatthe present invention provides an apparatus for polishing a wafer whichcan more stably load and unload the wafer by absorbing and chucking itby vacuum.

Also, the present invention can prevent a certain portion of a waferfrom being over-polished by imposing uniformly load on a rear surface ofthe wafer in a polishing process.

Further, the present invention can easily control load to be imposed oncertain areas of a wafer by providing a plurality of spaces separatedfrom each other by means of supporters and membranes, and therebyprecisely control the polishing speed of the certain portions of thewafer.

Still further, the present invention can prevent scratches from beinggenerated due to the polishing head by cleansing slurry particlesflowing in between membranes and supporters during the polishingprocess.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor the purpose of limitation, the scope of the invention being setforth in the following claims.

1. A method for polishing a wafer, comprising the steps of:vacuum-absorbing a wafer through a vacuum hole of a membrane positionedunder a polishing head; locating the vacuum-absorbed wafer on apolishing pad; and polishing the wafer.
 2. The method of claim 1 whereinvacuum-absorbing comprises drawing a vacuum on a fluid path formedthrough a supporter of the polishing head on which the membrane ismounted.
 3. The method of claim 2 wherein the vacuum hole of themembrane comprises multiple first vacuum holes and wherein the supporterincludes multiple second vacuum holes in alignment with the multiplefirst vacuum holes, and wherein the fluid path is in communication withthe multiple second vacuum holes.
 4. The method of claim 3 wherein,during vacuum absorbing, each of the first vacuum holes forms a sealabout the corresponding second vacuum hole.
 5. The method of claim 3wherein a plurality of film structures are disposed on an outer surfaceof the supporter about each of the multiple second holes, each of thefilms mating with the corresponding first vacuum hole formed in themembrane.
 6. The method of claim 1 wherein polishing the wafer isperformed by applying pressure to a region between the membrane and thepolishing head through the vacuum hole to place the wafer in contactwith the polishing head.
 7. The method of claim 1 wherein polishing thewafer comprises expanding the membrane to provide a uniform load overthe wafer.
 8. The method of claim 1 further comprising chucking thewafer, wherein the wafer is vacuum-absorbed through the vacuum hole andthe wafer is adhered to the membrane.
 9. The method of claim 8 furthercomprising an unloading the wafer, wherein pressure is applied to themembrane to release the wafer from the membrane.
 10. A method forpolishing a wafer, comprising the steps of: vacuum-absorbing a waferthrough a vacuum hole of a membrane positioned under a polishing head,wherein vacuum-absorbing comprises drawing a vacuum on a fluid pathformed through a supporter of the polishing head on which the membraneis mounted, wherein the vacuum hole of the membrane comprises multiplefirst vacuum holes and wherein the supporter includes multiple secondvacuum holes in alignment with the multiple first vacuum holes, andwherein the fluid path is in communication with the multiple secondvacuum holes, and wherein a plurality of film structures are disposed onan outer surface of the supporter about each of the multiple secondholes, each of the films mating with the corresponding first vacuum holeformed in the membrane; locating the vacuum-absorbed wafer on apolishing pad; and polishing the wafer.